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School of Molecular & Biomedical Science |
Trichophyton equinumOn Sabouraud's dextrose agar, colonies are usually flat, but some may develop gentle folds or radial grooves, white to buff in colour, suede-like to downy in texture, and are similar to T. mentagrophytes. Cultures usually have a deep-yellow submerged fringe and reverse which later becomes dark red in the centre. Microscopically, abundant microconidia which may be clavate to pyriform and sessile or spherical and stalked are formed laterally along the hyphae. Macroconidia are only rarely produced, but when present are clavate, smooth, thin-walled and of variable size. Occasional nodular organs may be present and the microconidia often undergo a transformation to produce abundant chlamydoconidia in old cultures. RG-2 organism.
Kaminski's Dermatophyte Identification SchemeLittman Oxgall Agar (Difco): Compact, raised velvety white surface with yellowish reverse and diffusing yellow pigment. Lactritmel Agar (Mycopathologia 91:57-59, 1985): Flat spreading, white to cream-coloured, powdery to granular surface with a central downy papilla, and deep brownish red reverse. Microscopic morphology as described above for the primary culture. Sabouraud's Dextrose Agar with 5% NaCl: An extremely stunted, slow growing dark brown colony with a few submerged brown hyphae. 1% Peptone Agar: Flat white to cream, suede-like surface with raised white downy centre and pale yellow reverse. Hydrolysis of Urea: Positive in 4-5 days. Vitamin Free agar (Difco Trichophyton Agar No.1): Trichophyton equinum var. autotrophicum does not have any special nutritional requirements for growth ie. good growth on T1. Trichophyton equinum var. equinum has a complete growth requirement for nicotinic acid, ie. no growth on Trichophyton No. 1 but good growth on T5.
Hair Perforation Test ("in vitro"): Positive for T. equinum var. autotrophicum; but negative for Trichophyton equinum var. equinum. Clinical significance:Trichophyton equinum is a zoophilic fungus causing ringworm in horses and rare infections in humans. It is of world-wide distribution except for. var. autotrophicum which is restricted to Australia and New Zealand. Most strains require nicotinic acid for growth except those from Australia and New Zealand, which are autotrophic (var. autotrophicum). Invaded hairs show an ectothrix infection but do not fluoresce under Wood's ultra-violet light. Mycosis: DermatophytosisFurther reading:Rebell, G., and D. Taplin. 1970. The Dermatophytes. 2nd. revised edition. University of Miami Press, Coral Gables, Florida. USA. Rippon, J.W. 1988. Medical Mycology. 3rd Edition. W.B. Saunders Co., Philadelphia, USA.
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